On Fri, Jan 7, 2022 at 3:43 PM Raghavendra Rao Ananta
<rananta@xxxxxxxxxx> wrote:
>
> Hi Reiji,
>
> On Thu, Jan 6, 2022 at 10:07 PM Reiji Watanabe <reijiw@xxxxxxxxxx> wrote:
> >
> > Hi Raghu,
> >
> > On Tue, Jan 4, 2022 at 11:49 AM Raghavendra Rao Ananta
> > <rananta@xxxxxxxxxx> wrote:
> > >
> > > Capture the start of the KVM VM, which is basically the
> > > start of any vCPU run. This state of the VM is helpful
> > > in the upcoming patches to prevent user-space from
> > > configuring certain VM features after the VM has started
> > > running.
> > >
> > > Signed-off-by: Raghavendra Rao Ananta <rananta@xxxxxxxxxx>
> > > ---
> > > include/linux/kvm_host.h | 3 +++
> > > virt/kvm/kvm_main.c | 9 +++++++++
> > > 2 files changed, 12 insertions(+)
> > >
> > > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> > > index c310648cc8f1..d0bd8f7a026c 100644
> > > --- a/include/linux/kvm_host.h
> > > +++ b/include/linux/kvm_host.h
> > > @@ -623,6 +623,7 @@ struct kvm {
> > > struct notifier_block pm_notifier;
> > > #endif
> > > char stats_id[KVM_STATS_NAME_SIZE];
> > > + bool vm_started;
> >
> > Since KVM_RUN on any vCPUs doesn't necessarily mean that the VM
> > started yet, the name might be a bit misleading IMHO. I would
> > think 'has_run_once' or 'ran_once' might be more clear (?).
> >
> I always struggle with the names; but if you feel that 'ran_once'
> makes more sense for a reader, I can change it.
I would prefer 'ran_once'.
> > > };
> > >
> > > #define kvm_err(fmt, ...) \
> > > @@ -1666,6 +1667,8 @@ static inline bool kvm_check_request(int req, struct kvm_vcpu *vcpu)
> > > }
> > > }
> > >
> > > +#define kvm_vm_has_started(kvm) (kvm->vm_started)
> > > +
> > > extern bool kvm_rebooting;
> > >
> > > extern unsigned int halt_poll_ns;
> > > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> > > index 72c4e6b39389..962b91ac2064 100644
> > > --- a/virt/kvm/kvm_main.c
> > > +++ b/virt/kvm/kvm_main.c
> > > @@ -3686,6 +3686,7 @@ static long kvm_vcpu_ioctl(struct file *filp,
> > > int r;
> > > struct kvm_fpu *fpu = NULL;
> > > struct kvm_sregs *kvm_sregs = NULL;
> > > + struct kvm *kvm = vcpu->kvm;
> > >
> > > if (vcpu->kvm->mm != current->mm || vcpu->kvm->vm_dead)
> > > return -EIO;
> > > @@ -3723,6 +3724,14 @@ static long kvm_vcpu_ioctl(struct file *filp,
> > > if (oldpid)
> > > synchronize_rcu();
> > > put_pid(oldpid);
> > > +
> > > + /*
> > > + * Since we land here even on the first vCPU run,
> > > + * we can mark that the VM has started running.
> > > + */
> >
> > It might be nicer to add a comment why the code below gets kvm->lock.
> >
> I've been going back and forth on this one. Initially I considered
> simply going with atomic_t, but the patch 4/11 (KVM: arm64: Setup a
> framework for hypercall bitmap firmware registers)
> kvm_arm_set_fw_reg_bmap()'s implementation felt like we need a lock to
> have the whole 'is the register busy?' operation atomic. But, that's
> just one of the applications.
I understand why you need the code to get the lock here with the
current implementation.
But, since the code just set the one field (vm_started) with the lock,
I thought the intention of getting the lock might not be so obvious.
(But, maybe clear enough looking at the code in the patch-4)
Thanks,
Reiji
> > Anyway, the patch generally looks good to me, and thank you
> > for making this change (it works for my purpose as well).
> >
> > Reviewed-by: Reiji Watanabe <reijiw@xxxxxxxxxx>
> >
> Glad that it's helping you as well and thanks for the review.
>
> Regards,
> Raghavendra
>
> > Thanks,
> > Reiji
> >
> >
> > > + mutex_lock(&kvm->lock);
> > > + kvm->vm_started = true;
> > > + mutex_unlock(&kvm->lock);
> > > }
> > > r = kvm_arch_vcpu_ioctl_run(vcpu);
> > > trace_kvm_userspace_exit(vcpu->run->exit_reason, r);
> > > --
> > > 2.34.1.448.ga2b2bfdf31-goog
> > >
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